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Tom Kyte

Thanks for the question, rd.

Asked: August 09, 2001 - 4:25 pm UTC

Last updated: March 12, 2004 - 5:23 pm UTC

Version: 8.1.5

Viewed 1000+ times

You Asked

Tom

is there any difference between using <> and !=,if so which one is better.

what is the difference between using 'yyyy' and 'rrrr' in the date format for years?


instead of

AND (a.cc_cd IN ('aus','eng','ind') OR b.sec_cc_cd IN ('aus','eng','ind'))

can I do

AND a.cc_cd or b.sec_cc_cd in ('aus','eng','ind')

can you discuss a similar example for me, and illustrate


If the optimizer is set to choose, will the optmizer automatically choose cbo when we use full or first_rows hint, what are the hints which are valid for rbo.



and Tom said...

they are the same <> and !=

one defaults the century, the other does not:


1 select 'yyyy 99', to_char( to_date( '99', 'yyyy' ), 'yyyy' ) from dual
2 union all
3 select 'rrrr 99', to_char( to_date( '99', 'rrrr' ), 'yyyy' ) from dual
4 union all
5 select 'yyyy 01', to_char( to_date( '1', 'yyyy' ), 'yyyy' ) from dual
6 union all
7* select 'rrrr 01', to_char( to_date( '1', 'rrrr' ), 'yyyy' ) from dual
ops$tkyte@ORA817.US.ORACLE.COM> /

'YYYY99 TO_C
------- ----
yyyy 99 0099
rrrr 99 1999
yyyy 01 0001
rrrr 01 2001

ops$tkyte@ORA817.US.ORACLE.COM>

No, you cannot do "a or b in (x,y,z)" instead of "a in (x,y,z) or b in (x,y,z)"

Regardless of the optimizer goal set, if you use a HINT you will be using the CBO -- period.

The only valid "hint" for RBO is /*+ RULE */ -- telling the optimizer to use RBO. There are no hints available for RBO.



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Comments

But still some confusion

Jon, March 12, 2004 - 1:01 pm UTC

I was having a discussion with someone about "rounded years" and so I came to the expert. I guess I don't understand the purpose of RRRR. The documentation say, "Accepts either 4-digit or 2-digit input (apparently 1-digit also from your example). If 2-digit, provides the same return as RR. If you don't want this functionality, then simply enter the 4-digit year." Since 2-digit input gives you the same functionality as 4-digit, why not just enter RR (since the whole purpose of this seems to be to accommodate lazy people who don't want to enter a 4-digit year. And if you're going to do it right (IMHO) and enter the full four digits, who needs RRRR since we have YYYY.

This RRRR thing looks like a Y2.05K problem in the making. I say enter the 4 digits and use YYYY. Am I missing something?

Tom Kyte
March 12, 2004 - 5:23 pm UTC

I say enter 4 digits period. whether you use rrrr or yyyy at that point is no longer relevant.

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